A computer program listing appendix xe2x80x9cAxe2x80x9d on a compact disc is included and the material of the disc incorporated herein by reference. A total of two (2) compact discs are submitted, one original and one duplicate identified as xe2x80x9cCopy 1xe2x80x9d and xe2x80x9cCopy 2xe2x80x9d and the single file on each is identified as xe2x80x9c2000157Discxe2x80x9d. The program was written in FORTRAN 77 and runs on a Unix based SUN computer.
The invention relates to a method and algorithm for predicting fluid loss from a system.
When pneumatic tires were first invented, maintenance of the tires on a vehicle was a continuing duty of the vehicle operator. Several extra spares were carried at all times, and ensuring the proper inflation of the tires was an almost daily routine.
As tires have developed, it has been a continued goal to build tires that are substantially maintenance free. Toward this goal, better sealing arrangements have been developed between the tire and the rim, better tire valves have been developed, and more flexible less permeable rubbers have been developed. In some better made tires, a liner of butyl rubber (BR) is placed in the inner cavity of the tire to further reduce the air permeability of the tire construction.
Currently, it is common for the vehicle operator to test air pressure in a tire only when a tire looks low, and scheduled maintenance for a passenger tire may require only that the air pressure be checked every one to three months.
In most modern passenger tires, it is considered a defect if a tire loses 3% or more of its inflation pressure per month.
Accordingly, air retention tests have been developed to check how well particular tire builds retain inflation pressure.
Some early air retention tests needed as much as 180 days to complete. By various accelerating techniques, some such tests have been reduced to 60 days.
Even at 60 days, the term of the test is considered by many to be too long, since if there is a defect in the design, or a defect in one of the materials used in the tire, 60 days of tires may be built before the defect is discovered. Because of this, those in the art have been continuously trying to further accelerate air retention testing.
A number of attempts have been made to accelerate air retention testing by substituting helium for air in the test. Helium has a high diffusion rate through rubber, and escapes from a tire much faster than air. In the previous attempts, however, it was only possible to observe the time it took for a tire to go flat when inflated with helium, and no specific data on leakage rates could be obtained.
In copending Application Ser. No. 09/668,115, now U.S. Pat. No. 6,393,897 herewith, the inventor has provided an apparatus that makes possible to use of helium in an accelerated air leakage test, where parameters are observed that make possible the determination of leakage rates.
It is an object of this invention to provide a method and algorithm for calculating air leakage rates for tires, using data from helium leakage from the tires.
Other objects of the invention will be apparent from the following description and claims.
A method for calculating system fluid loss from a system based on measured fluid loss of a substitute fluid comprises the steps of (a) obtaining data over time for fluid loss of a substitute fluid in a system, (b) using the data to calculate a rate factor f for the substitute fluid which defines the factor by which the leak rate of the substitute fluid is different from the leak rate of the system fluid, (c) using the calculated rate factor f with the gas law equation PV=nRT to calculate the expected system fluid loss in the system. The method may include the further step of comparing the calculated rate factor f with rate factors f determined previously by experiment.
The method can also be used to compare the calculated system fluid loss with a predetermined value.
In more sophisticated embodiments of the invention, the method may include the further step of providing a first signal if the calculated value is acceptable as compared to the predetermined value, and providing a second signal if the calculated value is not acceptable as compared to the predetermined value.
The method may include the further steps of (a) calculating data for the substitute fluid for loss per month, change in concentration with time, pressure, system inner volume, system outer volume, and container volume, as well as, when the test object is a tire, calculating data for liner butyl rubber (BR) content, distance of the liner ending from the toe of the tire, and the liner gauge.
The method may include the further step of calculating a mean factor for f, and calculating build to build differences by convergence and optimizing slopes. The mean actor f provides a basis of comparison when one accounts for liner composition, gauge and ending position when the system is a pneumatic tire.
The method may include outputting measurements for the substitute fluid and the prediction for the system fluid.
A specific algorithm to carry out the method is also provided.